A nonaqueous electrolyte battery in which a lithium metal, a lithium alloy, a lithium compound or a carbonaceous material is used for a negative electrode is expected as a high energy density battery, and active research and development have been conducted. A lithium ion secondary battery comprising a positive electrode containing LiCoO2 or LiMn2O4 as an active material and a negative electrode containing a carbonaceous material that allows lithium ions to be inserted and extracted has been widely put to practical use for a portable device.
In the case of installing the battery in a vehicle such as an automobile or a train, it is preferable that the positive and negative electrodes are formed of a material excellent in chemical and electrochemical stability, in strength, and in corrosion resistance in view of storage performance in high-temperature environments (at not less than 60° C.), cycle performance, and reliability of high power over a long time. Further, high performance in cold climates, high-output performance in a low-temperature environment (−40° C.), and long life performance are required. On the other hand, although a nonvolatile and noncombustible electrolytic solution has been developed as a nonaqueous electrolyte from the viewpoint of enhancing safety performance, a battery inclusing the electrolytic solution has not yet been put to practical use because output characteristics, low-temperature performance, and long life performance are reduced.
As described above, when the lithium ion secondary battery is installed in a vehicle or the like, there is a problem in high-temperature durability and low-temperature output performance. Thus, it is difficult to install the lithium ion secondary battery on an engine room of the vehicle in place of a lead storage battery.
Since an electrolytic solution of the lithium ion secondary battery is used at a high voltage of 2 V to 4.5 V, an aqueous solution-based electrolytic solution is not used in the electrolytic solution of the lithium ion secondary battery, and a nonaqueous electrolytic solution in which lithium salt is dissolved in an organic solvent is used. It has been considered to improve a composition of the nonaqueous electrolytic solution and thereby improve large current discharge performance and cycle life performance. However, since ion conductivity of the nonaqueous electrolytic solution is lower than that of the aqueous solution-based electrolytic solution, it is difficult to lower the resistance of a battery. Since an organic solvent is used, high temperature decomposition is likely to occur, and since heat stability is poor, high-temperature cycle life performance is lowered. Thus, although a solid electrolyte has been considered as a nonaqueous electrolyte, since the ion conductivity of the nonaqueous electrolyte is further lowered, it is difficult to improve large current discharge performance.